A transportation funding proposal from the president of the Maryland Senate not only would impose a 3 percent sales tax on gasoline, but also calls for an automatic, 5-cents-per-gallon gas tax that could be controlled by the counties or the state.

The latter tax could be used to raise money for county transportation projects, but would be imposed whether the counties want it or not, a State House aide confirmed.

According to the bill, introduced Tuesday by Senate President Thomas V. Mike Miller Jr. (D-Dist. 27) of Chesapeake Beach, each county has the option of imposing the tax at the wholesale level starting in 2017. But if the imposed rate is less than 5 cents per gallon, the state will collect the difference — meaning if the county rate was 3 cents per gallon, the state would collect the remaining 2 cents.

This principle would apply even if a county decided not to impose the additional tax; in that case, the full 5 cents would go to the state’s Transportation Trust Fund, according to the aide.

Only by implementing the tax themselves will county governments be able to control how that revenue is spent, the aide said.

Miller has acknowledged that the provisions in his bill — which include establishing up to two regional transit authorities that would oversee the funding and development of mass transit projects in the Baltimore and Washington, D.C., metropolitan regions — will be a tough sell.

The bill also establishes a 3 percent sales tax on the wholesale cost of gasoline, to be levied on top of the state’s existing 23.5-cent-per-gallon gas tax.

Miller has called for Gov. Martin O’Malley (D), who did not include a transportation proposal in his legislative package this year, to take a more active role in the matter.

“I’m sure that if he decides he wants to work, and work hard, he can get this done,” Miller said.